1. Field of the Invention
This invention relates to a zoom lens barrel assembly for a camera, and, more particularly, to a power driven zoom lens barrel assembly for a camera which is operated by a single power drive device to achieve both adjusting a zoom ratio of the zoom lens and focusing the zoom lens.
2. Description of Related Art
In most zoom lenses, lens groups of the zoom lens are moved along optical axis by means of a cam mechanism differently between focusing the zoom lens on a subject and adjusting a zoom ratio of the zoom lens. To enable the zoom lens to achieve focusing and zooming in different manners, there have been proposed several techniques. Specifically, one of the techniques employs separate power drive devices such as electric motors for focusing and zoom ratio adjusting, respectively. Another technique employs a single power drive device. In the case where a single power drive device is used for both focusing and zoom ratio adjusting, there have been known several ways. One of them divides driving power from the single power drive device into two parts for focusing and zoom ratio adjusting. The second is, which is known from, for example, Japanese Patent Publication No. 6-100707, to incorporate a mechanism common to focusing and zoom ratio adjusting and to achieve focusing and zoom ratio adjusting alternately. Another one, which is known from, for example, Japanese Unexamined Patent Publication No. 9-43487, incorporates a restraint mechanism which causes relative axial movement along the optical axis between two lens groups of the zoom lens to achieve zoom ratio adjusting and locking axial movement of one of the two lens groups relative to the other during focusing.
The utilization of two power drive devices always yields an increase in camera price. The single power drive device cooperating with separate drive mechanisms for focusing and zoom ratio adjusting always needs an increased number of parts with an adverse effect of not only increasing costs but also increasing an overall size of the camera. The combination of a single power drive device and a common drive mechanism has a necessity for providing alternate lens guide cam slots for focusing and zoom ratio adjusting which makes a lens drive mechanism quite complex. While the last zoom lens drive system can remove the above drawbacks, however, the locking mechanism needs an electromagnetic solenoid to disconnect operative linkage between one of the two lens groups and its associated cam to lock the axial movement of the lens group and to hold the lens group with friction only so as to remain immovable, which possibly leads to unstable focusing operation.